Presently available spermicidal contraceptives contain ingredients including the neutral surfactants isononyl-phenyl-polyoxyethylene (9) ether or Nonoxynol-9 (N-9), p-menthanyl-phenyl-polyoxyethylene (8,8) ether or menfegol, isooctyl-phenyl-polyoxy-ethylene (9) ether or Octoxynol-9 (0-9) [K. Furuse, et al. J Pharmacobiodyn. 6: 359, 1983; G A Digenis, et al. Pharm Dev Technol.; 4: 421, 1999], etc. Of these, the most commonly used spermicidal contraceptive in the United Kingdom and the United States is N-9 [OTC Panel. Federal Register.; 45: 1980, 82014; E. Chantler. Brit Fam Plann.; 17, 118, 1992]. Other preparations/molecules under different phases of investigation are: Oxovanadium (IV) complexes of 1,10-Phenanthroline, 2,2′-Bipyridyl, 5′-Bromo-2′-Hydroxyacetophenone and derivatives [G A Digenis, et al. Pharm Dev Technol.: 4, 1999, 421]; Aryl Phosphate Derivative of Bromo-Methoxy Zidovudine (Compound WHI-07) [O. J D'Cruz., et al, Biology of Reproduction: 62, 2000, 37]; Lipophilic Vaginal Contraceptive Gel-Microemulsion, GM-144 [O J D'Cruz, et al. AAPS Pharm Sci Tech.; 2, article 5, 2001] and sodium nimidinate, the spermicidal agent of neem oil [DE Champagne, et al; Phytochemistry, 31, 377, 1992]. N-9 is being used at concentrations of 2% to 6% in creams and gels, 12% in foams, and as high as 18% in condom lubricants and 28% in vaginal contraceptive film. Frequent use of N-9 as a vaginal contraceptive/microbicide has been associated with an increased risk of vaginal or cervical infection, irritation, or ulceration [M L Rekart. J Acquir Immune Defic Syndr.; 5: 425, 1992, R E Roddy, et al. Int J STD HIV.; 4: 165, 1993, S S Weir, et al. Genitourin Med.; 71: 78, 1995]. In addition, it alters vaginal niche of bacteria or microflora, specially Lactobacilli and lead to an increased risk of opportunistic infections [T M Hooton, et al. JAMA.; 265: 64, 1991; M K Stafford, et al. J Acquir Immune Defic Syndr Hum Retrovirol.; 17: 327, 1998; I J Rosenstein, et al. J Infect Dis.; 177, 1386, 1998]. Such infections are known to enhance the susceptibility of the ectocervical epithelium and the endocervical mucosa to sexually transmitted pathogens including human immunodeficiency virus, type 1 (HIV-1) infection [J Kreiss, et al. JAMA.; 268, 477, 1992; M H Augenbraun, et al. Infect Dis Clin North Am.; 8: 439, 1994; EG Raymond, et al. Obstetrics & Gynecology.; 103, 430, 2004]. Frequent use of spermicidal vaginal foaming tablets containing menfegol is also associated with a high incidence of genital lesions [J Goeman, et al. J Infect Dis. 171, 1611, 1995]. Moreover, N-9 is composed of multiple oligomers that vary in ethyleneoxyde chain length and in biological performance [P. T. Fowler, et al AAPS Pharm Sci Tech 2003; 4(3) Article 30; B Walter, et al. Pharm Res, 1991; 8:409].
Thus, in short Nonoxynol-9 (N-9), the effective spermicidal molecule used widely in vaginal contraceptive formulations has been shown to render the user susceptible to STDs, including AIDS. The WHO has cautioned that N-9 containing formulations should not be used by those at risk of acquiring HIV infection.
Since heterosexual transmission of HIV-1 is the predominant mode of the epidemic spread of acquired immunodeficiency syndrome (AIDS), there is a pressing need to expedite research to get a safe, effective vaginal spermicidal product lacking strong toxicity and which may offer significant clinical advantage over the currently available medications in the market. A recent statement from the Medical Advisory Panel of the IPPF recommends that N-9 should be used only in combination with a mechanical barrier method and that condoms pre-lubricated with N-9 have no added advantage in contraceptive efficacy and should no longer be distributed to women at high risk of HIV/AIDS [IPPF Medical Bulletin, 37, 1, 2003].
India is one of the 12 mega-diversity countries in the world with a vital stake in conservation and sustainable utilization of its biodiversity resources. It is rich in vegetation of medicinal plants. One of such plants, Acacia auriculiformis (English: Earleaf Acacia, and Akashmoni/Sonajhuri in Bengali and Hindi), is a loose, rounded, evergreen, roadside or wild tree. The tree is also available in other parts of the world. The use of extracts from seeds of the tree is reported from time to time. The major components of the extracts are saponins of different kinds.
Herbal saponins are in use since the early age of human civilization specially for making toiletries. Some other medicinal properties of the saponins are also noted by different workers. Acaciaside-A and Ac-B, two acylated bisglycoside saponins originally isolated from the seeds of Acacia auriculiformis (B C Pal, et al. Indian Patent No. 186738] are known to have anti-helminthic activity [N K Ghosh, et al. J Helminthol. 70, 171, 1996]. Mandal et al. [Fitoterapia, 76, 462, 2005] reported that complete inhibition of conidial germination of Aspergillus ochraceous and Curvularia lunata was recorded at 300 μg/ml or less; whereas 700 μg/ml or higher concentrations of the mixture was required to inhibit the growth of Bacillus megaterium, Salmonella typhimurium and Pseudomonas aeruginosa. The conjugated unsaturated diene system of the saponins is likely to be involved in producing their damaging effect, probably by generation of free radicals that induce membrane damage through peroxidation [S P Sinha Babu, et al. Jpn J Pharmacolm. 75, 451, 1997; B Nandi, et al. Phytother Res., 18, 191. 2004]. Some other investigations suggest that the plant may contain active antimutagenic and chemopreventive agents [K. Kaur, et al Willd. Ex Del. Drug Chem Toxicol.; 25, 39, 2002] and antifilarial effect [M, Ghosh, et al Indian J Exp Biol. 31, 604, 1993; S B Mahato Adv Exp Med Biol. 404, 173, 1996]. A mixture of Acaciaside-A and Ac-B was reported to kill in vitro 97% microfilaria of Setaria cervi in 100 min at 4 mg/ml concentration and 100% of adults in 35 min. Farnsworth et al. reported that the majority of triterpine saponins, obtained from the plants, possess spermicidal properties [Research frontiers in fertility regulation 2, 1, 1982]. Setty et al reported that saponins, isolated from Indian medicinal plants, may act as potential spermicides [B S Setty, et al. Contraception 14: 571, 1976]. A series of bioactive triterpenoid saponins were characterized by a stringent structure-activity and were reported to be potent and selective inhibitors of human immunodeficiency virus type 1 (HIV-1) replication [Yang X W; et al. J Nat Prod. 1999: 62(11):1510-3].
A mixture of two analogous triterpenoid glycosides, Acaciaside-A and Ac-B, isolated from the seeds of Acacia auriculiformis, was reported to possess strong in vitro spermicidal property on human spermatozoa [A, Pakrashi, et al., Contraception 43: 475, 1991]. But a serious disadvantage of considering the mixture for formulation is that the MEC in humans is much higher (350 μg/ml) than that of pure Ac-B (125 μg/ml) [H Ray, et al., Unpublished observation]. Moreover, one of its major constituents (i.e. Acaciaside-A) is a mutagen.
The most intriguing aspect of Ac-B, however, is that its spermicidal effects involve damage of lipid molecules of the cell membrane [H Ray, et al., Unpublished Observation]. HIV requires intact lipid rafts, highly specialized sub-regions in cell membranes, for entry into cells and budding of fully infectious particles. By virtue of its lipid dispersing effects, Ac-B is likely to disrupt the lipid rafts as well as the lipid molecules of viral envelop and therefore, theoretically appears to be a likely prophylactic candidate for HIV infection.